(1) Field of the Invention
The present invention relates to a ball point pen and, more particularly, to a ball point pen which is ready to be employed for writing when the front end of the pen is oriented downward to thereby project the tip of a cartridge from a ball point pen main body and which is, on the other hand, capable of automatically accommodating the tip of the cartridge inside the ball point pen main body when the front end of the ball point pen main body is oriented upward.
(2) Description of the Prior Art
A ball point pen is conventionally known in which the tip of a cartridge, which engage an engaging step arranged inside the ball point pen main body when the tip of the cartridge accommodated inside the main body, is projected therefrom, so that retraction of the cartridge into the main body may be prevented and writing may be easily performed. However, with a ball point pen of this type, when the tip of the cartridge is projected from the main body, the tip of the cartridge must engage with the engaging step inside the main body without failure to prevent the retraction of the cartridge into the main body.
During writing, however, the tip of the cartridge is constantly brought into contact with and withdrawn from a sheet of paper, and pressure is exerted on the cartridge from various directions. With a conventional ball point pen, the force of gravity of the cartridge acts along the axial direction. Therefore, especially when the ball point pen is used under the condition that it is almost vertical with respect to the plane of the paper, the cartridge swings in an unstable manner inside the ball point pen main body and the engagement between the tip of the cartridge and the engaging step inside the main body may be easily disturbed when the tip of the cartridge is withdrawn from the sheet of paper. In such a case, when the tip of the cartridge is again pressed against the sheet of paper, the cartridge tends to become retracted into the main body.